Use of porous glass media for a biofilter to remove odorous compounds from an air stream

ABSTRACT

A system for removing undesirable compounds from contaminated air includes a biofilter having porous glass media. Hydrogen sulfide is removed from contaminated air by passing the contaminated air through the biofilter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 120 as a continuationof U.S. patent application Ser. No. 16/165,045 filed Oct. 19, 2018,titled USE OF POROUS GLASS MEDIA FOR A BIOFILTER TO REMOVE ODOROUSCOMPOUNDS FROM AN AIR STREAM, now U.S. Pat. No. 10,730,013, issued Aug.4, 2020; which is a division of U.S. application Ser. No. 14/920,407,filed Oct. 22, 2015, titled USE OF POROUS GLASS MEDIA FOR A BIOFILTER TOREMOVE ODOROUS COMPOUNDS FROM AN AIR STREAM, now U.S. Pat. No.10,159,932, issued Dec. 25, 2018, which claims the benefit of U.S.Provisional Application Ser. No. 62/084,007, filed Nov. 26, 2014, andwhich is a continuation-in-part of U.S. application Ser. No. 14/270,461,filed May 6, 2014, titled USE OF FOAMED GLASS AS MEDIA FOR A BIOFILTERTO REMOVE ODOROUS COMPOUNDS FROM AN AIR STREAM, the content of eachbeing incorporated herein by reference for all purposes.

BACKGROUND Field of Invention

Aspects and embodiments of the present invention are directed totreatment of air streams, and more particularly, to systems and methodsfor removing odor causing compounds from an air stream.

Discussion of Related Art

Sewage systems typically include conduits that collect and direct sewageand other waste streams, such as industrial effluents, to a treatmentfacility. Such systems typically include various pumping facilities,such as lift stations, that facilitate the transfer of wastewater tosuch treatment facilities. During transit odorous species are oftengenerated. Such odorous species may be objectionable when released ordischarged. Untreated sewage may generate multiple odor-causingcompounds. One of the most prevalent and most distinctive compoundsformed is hydrogen sulfide (H₂S).

Hydrogen sulfide may be formed in wastewater streams by the conversionof sulfates to sulfides by sulfide reducing bacteria (SRBs) underanaerobic conditions. Hydrogen sulfide is dissolvable in water (up toabout 0.4 g/100 ml at 20 degrees Celsius and 1 atmosphere of pressure).In water, hydrogen sulfide exists in equilibrium with the bisulfide ionHS⁻ and the sulfide ion S²⁻. Unlike sulfide and bisulfide, hydrogensulfide is volatile, with a vapor pressure of about 1.56×10⁴ mm Hg (2.1MPa) at 25 degrees Celsius, and may emerge from aqueous solution to formgaseous hydrogen sulfide. The presence of hydrogen sulfide in sewersystems is undesirable due to its offensive odor, toxicity, andcorrosivity.

Gaseous hydrogen sulfide exhibits a characteristic unpleasant odorsuggestive of rotten eggs. Humans can detect this odor at hydrogensulfide concentrations as low as four parts per billion (ppb). Hydrogensulfide is considered toxic. The United States Occupational Safety andHealth Administration (OSHA) has established a permissible exposurelimit to hydrogen sulfide (8 hour time-weighted average) of 10 ppm.Extended exposure to a few hundred ppm can cause unconsciousness anddeath. Accordingly, the presence of hydrogen sulfide in sewer systems isfound objectionable to people who may come into contact with the gaseouseffluent from such sewer systems.

Hydrogen sulfide also supports the growth of organisms such as thiothrixand beggiatoa. These are filamentous organisms which are associated withbulking problems in activated sludge treatment systems.

SUMMARY

In accordance with an aspect of the present invention, there is provideda gas phase biofilter for the treatment of contaminated air. Thebiofilter comprises a contaminated air inlet, a treated air outlet, anda media bed including foamed glass media in fluid communication betweenthe contaminated air inlet and the treated air outlet.

In some embodiments, the foamed glass media comprises silicon dioxide.The foamed glass media may include surface pores. The foamed glass mediamay include internal voids. Individual pieces of the foamed glass mediamay include passageways extending from first surfaces of the individualpieces to second surfaces of the individual pieces. The foamed glassmedia may comprise recycled glass.

In some embodiments, the biofilter further comprises a population ofhydrogen sulfide oxidizing bacteria disposed on and/or in the foamedglass media.

In some embodiments, the biofilter is operable to reduce a concentrationof hydrogen sulfide in contaminated air by more than about 95% when thecontaminated air is passed through the media bed of the biofilter at aflow rate of from zero to 500 cubic meters per hour per cubic meter ofmedia bed volume.

In some embodiments, the biofilter is operable to reduce theconcentration of hydrogen sulfide in the contaminated air by more thanabout 95% when the contaminated air is passed through the media bed ofthe biofilter at a flow rate of greater than about 500 cubic meters perhour per cubic meter of media bed volume.

In some embodiments, the biofilter is operable to reduce theconcentration of hydrogen sulfide in the contaminated air by more thanabout 99% when the contaminated air is passed through the media bed ofthe biofilter at a flow rate of from zero to 500 cubic meters per hourper cubic meter of media bed volume.

In some embodiments, the biofilter is operable to reduce theconcentration of hydrogen sulfide in the contaminated air by more thanabout 99% when the contaminated air is passed through the media bed ofthe biofilter at a flow rate of greater than about 500 cubic meters perhour per cubic meter of media bed volume.

In accordance with another aspect, there is provided a method ofremoving an undesirable compound from contaminated air. The methodcomprises flowing the contaminated air through a gas phase biofilterincluding a foamed glass media.

In some embodiments, the method further comprises filling a media bedcompartment of the biofilter at least partially with the foamed glassmedia prior to flowing the contaminated air through the biofilter.

In some embodiments, the method further comprises growing a populationof hydrogen sulfide oxidizing bacteria on the foamed glass media. Themethod may further comprise maintaining the population of hydrogensulfide oxidizing bacteria on the foamed glass media.

In some embodiments, the method further comprises measuring a one of aconcentration of nutrient in a fluid within and exiting the biofilterand adjusting an amount of nutrient added to the media bed compartmentper unit of time responsive to the concentration of the nutrient in thefluid being outside of a predetermined range.

In some embodiments, removing the undesirable compound from thecontaminated air comprises removing hydrogen sulfide from thecontaminated air. Removing the hydrogen sulfide from the contaminatedair may comprise reducing a concentration of hydrogen sulfide in thecontaminated air by more than about 95% by passing the contaminated airat a flow rate of from about zero to about 250 cubic meters per hour percubic meter of a media bed of the biofilter including the foamed glassmedia through the media bed. Reducing the concentration of hydrogensulfide in the contaminated air may comprise reducing the concentrationof hydrogen sulfide in the contaminated air by more than about 99%.Removing the hydrogen sulfide from the contaminated air may comprisesreducing a concentration of hydrogen sulfide in the contaminated air bymore than about 95% or by more than about 99% by passing thecontaminated air at a flow rate of greater than about 500 cubic metersper hour per cubic meter of the media bed through the media bed.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1A is a schematic diagram of a biofilter for treating acontaminated air stream;

FIG. 1B is a schematic diagram of another biofilter for treating acontaminated air stream;

FIG. 2 is a block diagram of a computer system upon which embodiments ofa method for treating a contaminated air stream may be performed;

FIG. 3 is a block diagram of a memory system of the computer system ofFIG. 2;

FIG. 4A is an image of an embodiment of a sintered glass biofiltermedia;

FIG. 4B is an image of another embodiment of a sintered glass biofiltermedia;

FIG. 5 is an image of an embodiment of a foamed glass biofilter media;

FIG. 6A is a scanning electron microscope micrograph of the surface ofan embodiment of a foamed glass biofilter media;

FIG. 6B is a scanning electron microscope micrograph of the surface ofan embodiment of a foamed glass biofilter media;

FIG. 6C is a scanning electron microscope micrograph of the surface ofan embodiment of a foamed glass biofilter media;

FIG. 6D is a scanning electron microscope micrograph of the surface ofan embodiment of a foamed glass biofilter media;

FIG. 6E is a scanning electron microscope micrograph of the surface ofan embodiment of a foamed glass biofilter media;

FIG. 6F is a scanning electron microscope micrograph of the surface ofan embodiment of a foamed glass biofilter media;

FIG. 7 is a flowchart of an embodiment of a method for treating acontaminated air stream using an embodiment of a biofilter as disclosedherein;

FIG. 8 is a chart of data obtained during testing of an embodiment of abiofilter including sintered glass biofilter media as disclosed herein;

FIG. 9 is another chart of data obtained during testing of an embodimentof a biofilter including sintered glass biofilter media as disclosedherein;

FIG. 10 is another chart of data obtained during testing of anembodiment of a biofilter including sintered glass biofilter media asdisclosed herein;

FIG. 11 is another chart of data obtained during testing of anembodiment of a biofilter including sintered glass biofilter media asdisclosed herein;

FIG. 12 is another chart of data obtained during testing of anembodiment of a biofilter including sintered glass biofilter media asdisclosed herein;

FIG. 13 is a chart of data obtained during testing of an embodiment of abiofilter including foamed glass biofilter media as disclosed herein;

FIG. 14 is another chart of data obtained during testing of anotherembodiment of a biofilter including foamed glass biofilter media asdisclosed herein; and

FIG. 15 is another chart of data obtained during testing of anotherembodiment of a biofilter including foamed glass biofilter media asdisclosed herein.

DETAILED DESCRIPTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” “having,” “containing,”“involving,” and variations thereof herein is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems.

It is generally desirable to remove hydrogen sulfide from air streams(referred to herein as “foul air”) from sewage systems, manholeheadspaces, wastewater treatment systems, and/or other systems in whichhydrogen sulfide may be generated. Aspects and embodiments disclosedherein include systems and methods for removing hydrogen sulfide fromcontaminated air streams. Aspects and embodiments disclosed herein mayalso be utilized to remove other objectionable and/or odor causingcompounds from contaminated air streams, for example, compoundsresulting from the volatilization of reduced sulfur compounds in asewage or wastewater stream such as any one or more of carbon disulfide,dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, methylmercaptans, ethyl mercaptans, butyl mercaptans, allyl mercaptans, propylmercaptans, crotyl mercaptans, benzyl mercaptans, thiophenol, sulfurdioxide, and carbon oxysulfide, or hydrogen sulfide generated from anyof these compounds by sulfate reducing bacteria. For the sake ofsimplicity, however, aspects and embodiments disclosed herein will bedescribed as removing hydrogen sulfide from contaminated gas streams.

Aspects and embodiments disclosed herein may remove hydrogen sulfidefrom contaminated gas stream by the biological conversion of thehydrogen sulfide into less objectionable or less odorous compounds. Insome embodiments, hydrogen sulfide oxidizing bacteria, for example, oneor more of ancalochloris beggiatoa, beggiatoa alba, sulfobacillus,thiobacillus denitrificans, thiohalocapsa halophila, thiomargarita, orthioploca oxidize hydrogen sulfide (H₂S) into sulfuric acid (H₂SO₄). Insome embodiments, the hydrogen sulfide oxidizing bacteria (referred tohereinafter as simply “bacteria”), are present on a media materialdisposed in a biofilter. The bacteria may form a biofilm on surfaces ofthe media material. Contaminated air passed through the biofiltercontacts the bacteria contained therein and the bacteria remove hydrogensulfide from the contaminated air by oxidizing the hydrogen sulfide intosulfuric acid. In some embodiments, the biofilter is supplied with waterand various nutrients, for example, nitrate, potassium, and phosphatecompounds, to provide an environment within the biofilter conducive forthe maintenance and/or growth of desirable bacteria populations. Thesupply of water and nutrients to the biofilter is, in some embodiments,controlled in response to the results of measurements of parametersincluding, for example, pH and nutrient concentration of liquid withinvarious portions of the biofilter and/or of waste liquid drained fromthe biofilter.

In new installations, bacteria may migrate into a new biofilter alongwith water vapor from an environment in which the new biofilter isinstalled to establish a bacterial population effective for the removalof odorous compounds from contaminated air from the environment. Theestablishment of a sufficiently large bacterial population within thebiofilter (referred to herein as “acclimation” of the biofilter) maytake between about a few days and about a week. In some implementations,a biofilter may be “seeded” with desirable bacteria to shorten the timeperiod required for the biofilter to acclimate.

FIG. 1A illustrates one embodiment of a biofilter, indicated generallyat 100A, for the treatment of contaminated air. The biofilter 100A issupplied with contaminated air 105, for example, air from the headspaceof a sewage system or a wastewater treatment system. The contaminatedair 105 contains odorous compounds including, for example, hydrogensulfide. The contaminated air 105 is blown through a blower 110 andthrough an air inlet 195 into a lower plenum 115 of a biofilter vessel120. In some embodiments, dilution air 107 may be provided to thebiofilter vessel 120 in addition to the contaminated air 105. Thedilution air 107 may be supplied through the same blower 110 as thecontaminated air 105 or a different blower. Dilution air 107 may beuseful in instances in which a concentration of hydrogen sulfide in thecontaminated air 105 exhibits a spike or otherwise exceeds a designconcentration for the biofilter 100A. Alternatively or additionally, thecontaminated air 105, along with any dilution air 107, may be pulledthrough the biofilter vessel 120 by a fan or blower located at an outlet150 of the biofilter vessel 120.

The contaminated air passes through the lower plenum 115 and into amedia bed compartment 125 of the biofilter 100A. The media bedcompartment 125 includes media, for example, particulate media, on whichbacteria and/or other microorganisms reside. The media is retained inthe media bed compartment 125 by a lower screen 130 and an upper screen135. In some embodiments, the upper screen 135 is omitted. Thecontaminated air passing through the media bed compartment 125 contactsthe media and the bacteria and/or other microorganisms on the media inthe media bed compartment 125. The bacteria and/or other microorganismsin the media bed compartment 125 consume hydrogen sulfide in thecontaminated air, removing the hydrogen sulfide from the contaminatedair and converting the contaminated air into treated air. The treatedair passes through an upper plenum 140 of the biofilter 100A and isreleased to the external environment 145 or a polishing unit through theupper gas outlet 150 of the biofilter vessel 120. In some embodiments, abiofilter may include multiple media compartments 125, for example, twomedia bed compartments, a second media bed compartment disposed above afirst media bed compartment and separated from the first media bedcompartment by appropriate screens or other separators.

Sulfuric acid and/or other acids produced by the bacteria and/or othermicroorganisms, water, unutilized nutrients, and other waste fluids exitthe biofilter vessel 120 through a drain outlet 170 and drain line 172.These waste fluids may be returned to a sewage system or wastewatertreatment system from which the contaminated air was withdrawn or may beotherwise treated, for example, to neutralize the acid in the wastefluids, or disposed of.

A lower portion of the plenum 115 may function as a sump which mayretain fluid 117 draining from the media bed compartment 125. The fluid117 may exit the biofilter vessel 120 once the level of the fluid 117reaches the level of the drain outlet 170.

To provide an environment conducive to the maintenance and/or growth ofa desirable bacterial/microbial population within the biofilter 100A,water from a source of water 155 and/or nutrients, for example, nitrate,potassium, and/or phosphate compounds from a source of nutrients 160 isintroduced into the biofilter vessel 120 through an inlet 165 of thebiofilter vessel 120. In some embodiments, the nutrients are supplied asan aqueous solution.

The source of water 155 and the source of nutrients 160 are illustratedin FIG. 1 as being in fluid communication with the same inlet 165 of thebiofilter vessel 120, but in other embodiments may be fluidly connectedto different inlets of the biofilter vessel 120. Upon entering thebiofilter vessel 120, the water and/or nutrients are distributed overthe top of the media bed in the media bed compartment 125 by, forexample, a fluid distributor, sprayer, or sprinkler (not shown). Inembodiments including multiple media beds, separate fluid distributorsmay be utilized to distribute water and/or nutrients over the respectivetops of the multiple media beds. The water and/or nutrients areperiodically provided to the media bed in the media bed compartment 125.In some embodiments, the water and/or nutrients are introduced into themedia bed in a timed interval. The timed interval and/or flow rate ofwater and/or nutrients into the media bed may vary in differentembodiments, and/or responsive to operating conditions of the biofilter100A as discussed below.

In some embodiments, the biofilter 100A is provided with one or moresensors which provide information to a controller 175. The controller175 analyzes the information from the one or more sensors and adjusts atiming/and or rate of introduction of water and/or nutrients from thesource of water 155 and/or source of nutrients 160, respectively, intothe biofilter vessel 120 responsive to an analysis of the information.In some embodiments, the controller 175 may also control a speed of theblower 110 and/or a ratio of contaminated air 105 to dilution air 107introduced into the biofilter responsive to an analysis of informationprovided from one or more sensors associated with the biofilter 100A,for example, a sensor providing information regarding a concentration ofH₂S exiting the biofilter 100A or a percent of H₂S removed fromcontaminated air by the biofilter. In some embodiments, the biofilter100A includes a pH sensor 180 and a nutrient concentration sensor 185configured to measure the pH and a concentration of one or morecomponents of a nutrient supplied to the biofilter 110A, respectively,in fluid within and/or drained from the biofilter vessel 120 through thedrain line 172. The sensors 180, 185 are illustrated as coupled to thedrain line 172 in FIG. 1A, but in other embodiments may be configured tomeasure parameters of fluid within the media bed 125, lower plenum 115,or other portions of the biofilter 100A.

The nutrient concentration measured by a nutrient sensor 185 is utilizedby the controller 175 to control a flow rate and/or frequency of theflow of nutrients from the source of nutrients 160 into the biofiltervessel 120. A nutrient concentration or a concentration of a componentof nutrient supplied to the biofilter 100A below a lower thresholdwithin the biofilter vessel 120 and/or exiting the drain 170 of thebiofilter vessel 120 may be indicative of insufficient nutrients beingsupplied to the bacteria. A nutrient concentration or a concentration ofa component of nutrient supplied to the biofilter 100A above an upperthreshold in fluid within the biofilter vessel 120 and/or exiting thedrain 170 of the biofilter vessel 120 may be indicative of an excessiveamount of nutrients being supplied to the bacteria. If the nutrientconcentration in fluid within the biofilter vessel 120 and/or exitingthe drain 170 of the biofilter vessel 120 is less than the lowerthreshold, the flow rate and/or frequency of the flow of nutrients fromthe source of nutrients 160 into the biofilter vessel 120 is increased.If the nutrient concentration in fluid within the biofilter vessel 120and/or exiting the drain 170 of the biofilter vessel 120 is above theupper threshold, the flow rate and/or frequency of the flow of nutrientsfrom the source of nutrients 160 into the biofilter vessel 120 isdecreased. In some embodiments, a nutrient concentration of, forexample, nitrate nitrogen (NO₃—N), of between about 5 mg/L and about 10mg/L in the sump of the biofilter or exiting the drain 170 of thebiofilter vessel 120 may be desirable.

In other embodiments, pH and nutrient concentration measurements aremanually taken from liquid 117 in the sump of the biofilter vessel andthe timing, rate, and/or volume of introduction of water and/ornutrients from the source of water 155 and/or source of nutrients 160,respectively are manually adjusted.

Pressure sensors 190 a, 190 b provide an indication of the differentialpressure across the biofilter vessel 120 and/or media bed compartment125. A pressure differential exceeding an upper threshold value, forexample, between about two inches (5.1 cm) and about 10 inches (25 cm)of water (four degrees Celsius) (between about 498 Pascal and about2,491 Pascal) or about 4 inches (10.2 cm, about 997 Pascal) of water maybe indicative of the biofilter vessel 120 and/or media bed compartment125 being blocked, for example, by contaminants or by over-packing ofmedia in the media bed compartment 125. Responsive to the detection of apressure differential exceeding an upper threshold, the controller 175may increase the speed of the blower 110 to maintain an air flow throughthe biofilter vessel 120 within a desired range and/or may shut down thebiofilter 100A and/or provide an indication to an operator that thebiofilter 100A may be in need of service. A pressure differential whichdecreases over time may be indicative of the biofilter vessel 120 and/ormedia bed compartment 125 exhibiting channeling, for example, due tochannels forming through the media bed and/or by poor distribution ormis-packing of media in the media bed compartment 125. Responsive to thedetection of a drop in the pressure differential, the controller 175 mayshut down the biofilter 100A and/or provide an indication to an operatorthat the biofilter 100A may be in need of service.

In some embodiments, as illustrated in the biofilter generally indicatedat 100B in FIG. 1B, which is substantially the same as biofilter 100A, aportion of the fluid 117 in the sump of the biofilter vessel 120 may berecycled, for example, from lower fluid outlet 174 through recycle line176 and pump 178 into an inlet 182 proximate an upper end of thebiofilter vessel 120. Residual nutrients remaining in the fluid exitingthe media bed 125 are thus re-introduced into the biofilter vessel 120,retaining the bioculture and reducing the need for “fresh” nutrients tobe introduced into the biofilter vessel 120 from the source of nutrients160, reducing operating costs of the biofilter 100B. Acid in the fluidexiting the media bed 125 is also re-introduced into the biofiltervessel 120, which may facilitate maintaining the pH within the media bed125 and/or biofilter vessel 120 at a desired level. Water and/ornutrients from the source of water 155 and/or source of nutrients 160,respectively, may be introduced into the biofilter vessel 120 throughthe same inlet 182 as the recycled liquid 117 and may be distributedonto the top of the media bed compartment 125 utilizing a common fluiddistributor, sprayer, or sprinkler as the recycled liquid 117.Biofilters configured as illustrated in FIG. 1B may be referred to astrickling biofilters. The following discussion applies equally to theboth biofilters 100A and 100B.

The controller 175 used for monitoring and controlling operation of thebiofilter 100A, 100B may include a computerized control system. Variousaspects of the invention may be implemented as specialized softwareexecuting in a general-purpose computer system 200 such as that shown inFIG. 2. The computer system 200 may include a processor 202 connected toone or more memory devices 204, such as a disk drive, solid statememory, or other device for storing data. Memory 204 is typically usedfor storing programs and data during operation of the computer system200. Components of computer system 200 may be coupled by aninterconnection mechanism 206, which may include one or more busses(e.g., between components that are integrated within a same machine)and/or a network (e.g., between components that reside on separatediscrete machines). The interconnection mechanism 206 enablescommunications (e.g., data, instructions) to be exchanged between systemcomponents of system 200. Computer system 200 also includes one or moreinput devices 208, for example, a keyboard, mouse, trackball,microphone, touch screen, and one or more output devices 210, forexample, a printing device, display screen, and/or speaker. The outputdevices 210 may also comprise valves, pumps, or switches which may beutilized to introduce water and/or nutrients from the source of water155 and/or the source of nutrients 160 into the biofilter and/or tocontrol the speed of a blower of the biofilter. One or more sensors 214may also provide input to the computer system 200. These sensors mayinclude, for example, nutrient sensor 185, pressure sensors 190 a, 190b, sensors for measuring a concentration of an undesirable component ofcontaminated air, for example, H₂S, and/or other sensors useful in abiofilter system. These sensors may be located in any portion of abiofilter system where they would be useful, for example, upstream of amedia bed, downstream of a media bed, in communication with a liquidwaste outlet of a biofilter vessel, and/or in communication with an airor gas outlet of a biofilter vessel. In addition, computer system 200may contain one or more interfaces (not shown) that connect computersystem 200 to a communication network in addition or as an alternativeto the interconnection mechanism 206.

The storage system 212, shown in greater detail in FIG. 3, typicallyincludes a computer readable and writeable nonvolatile recording medium302 in which signals are stored that define a program to be executed bythe processor or information to be processed by the program. The mediummay include, for example, a disk or flash memory. Typically, inoperation, the processor causes data to be read from the nonvolatilerecording medium 302 into another memory 304 that allows for fasteraccess to the information by the processor than does the medium 302.This memory 304 is typically a volatile, random access memory such as adynamic random access memory (DRAM) or static memory (SRAM). It may belocated in storage system 212, as shown, or in memory system 204. Theprocessor 202 generally manipulates the data within the integratedcircuit memory 204, 304 and then copies the data to the medium 302 afterprocessing is completed. A variety of mechanisms are known for managingdata movement between the medium 302 and the integrated circuit memoryelement 204, 304, and the invention is not limited thereto. Theinvention is not limited to a particular memory system 204 or storagesystem 212.

The computer system may include specially-programmed, special-purposehardware, for example, an application-specific integrated circuit(ASIC). Aspects of the invention may be implemented in software,hardware or firmware, or any combination thereof. Further, such methods,acts, systems, system elements and components thereof may be implementedas part of the computer system described above or as an independentcomponent.

Although computer system 200 is shown by way of example as one type ofcomputer system upon which various aspects of the invention may bepracticed, it should be appreciated that aspects of the invention arenot limited to being implemented on the computer system as shown in FIG.2. Various aspects of the invention may be practiced on one or morecomputers having a different architecture or components that that shownin FIG. 2.

Computer system 200 may be a general-purpose computer system that isprogrammable using a high-level computer programming language. Computersystem 200 may be also implemented using specially programmed, specialpurpose hardware. In computer system 200, processor 202 is typically acommercially available processor such as the well-known Pentium™ orCore™ class processors available from the Intel Corporation. Many otherprocessors are available. Such a processor usually executes an operatingsystem which may be, for example, the Windows 7 or Windows 8 operatingsystem available from the Microsoft Corporation, the MAC OS System Xavailable from Apple Computer, the Solaris Operating System availablefrom Sun Microsystems, or UNIX available from various sources. Manyother operating systems may be used.

The processor and operating system together define a computer platformfor which application programs in high-level programming languages arewritten. It should be understood that the invention is not limited to aparticular computer system platform, processor, operating system, ornetwork. Also, it should be apparent to those skilled in the art thatthe present invention is not limited to a specific programming languageor computer system. Further, it should be appreciated that otherappropriate programming languages and other appropriate computer systemscould also be used.

One or more portions of the computer system may be distributed acrossone or more computer systems (not shown) coupled to a communicationsnetwork. These computer systems also may be general-purpose computersystems. For example, various aspects of the invention may bedistributed among one or more computer systems configured to provide aservice (e.g., servers) to one or more client computers, or to performan overall task as part of a distributed system. For example, variousaspects of the invention may be performed on a client-server system thatincludes components distributed among one or more server systems thatperform various functions according to various embodiments of theinvention. These components may be executable, intermediate (e.g., IL)or interpreted (e.g., Java) code which communicate over a communicationnetwork (e.g., the Internet) using a communication protocol (e.g.,TCP/IP). In some embodiments one or more components of the computersystem 200 may communicate with one or more other components over awireless network, including, for example, a cellular telephone network.

It should be appreciated that the invention is not limited to executingon any particular system or group of systems. Also, it should beappreciated that the invention is not limited to any particulardistributed architecture, network, or communication protocol. Variousembodiments of the present invention may be programmed using anobject-oriented programming language, such as SmallTalk, Java, C++, Ada,or C # (C-Sharp). Other object-oriented programming languages may alsobe used. Alternatively, functional, scripting, and/or logicalprogramming languages may be used. Various aspects of the invention maybe implemented in a non-programmed environment (e.g., documents createdin HTML, XML or other format that, when viewed in a window of a browserprogram, render aspects of a graphical-user interface (GUI) or performother functions). Various aspects of the invention may be implemented asprogrammed or non-programmed elements, or any combination thereof.

The materials of construction of the biofilter vessel 120 are desirablyresistant to attack by acid which is generated by the bacteria in thebiofilter vessel 120. The walls of the biofilter vessel 120 and theupper and lower screens 130, 135 may be formed from, for example,fiberglass and/or an acid resistant polymer and/or may be coated with anacid resistant material.

Media used in the media bed compartment 125 of the biofilter vessel 120may be composed of various organic and/or inorganic materials,including, for example, wood mulch, pine bark, gravel, pumice, expandedshale, fired clay, and polymeric open celled foam (referred tohereinafter as “traditional media materials”). It has been discoveredthat media formed from these traditional media materials exhibitsvarious undesirable properties. For example, traditional media materialstypically degrade over time due to exposure to the acid environment in abiofilter vessel. Traditional media materials typically have usefullifetimes of between about one and about five years, after which theymust be replaced. If not replaced, traditional media materials such aswood mulch or pine bark may break down and form a sludge-like material,and gravel, pumice, shale, or fired clay may break down into sand-likeor clay-like particles. The sludge-like material or sand-like orclay-like particles may impede or block flow of contaminated air throughthe biofilter vessel. Traditional media materials typically areundesirably dense, rending handling difficult. Further, traditionalmedia materials often exhibit less than a desired odor removalefficiency due to, for example, limited surface area upon which bacteriamay grow. This low efficiency may require biofilters utilizingtraditional media materials to have a larger media bed, and thus alarger overall size than desired. Space is often at a premium in systemssuch as sewage lift stations and thus, it is desirable to providebiofilters having smaller rather than larger physical sizes for use insuch systems.

Media used in the media bed compartment of biofilters as disclosedherein may have certain desirable properties. For example, media for usein the media bed compartment of biofilters as disclosed herein desirablyhas a large surface area upon which hydrogen sulfide oxidizing bacteriamay reside. The media also is desirably resistant to decomposition ordamage by the hydrogen sulfide oxidizing bacteria, by hydrogen sulfideor other compounds present in the foul air treated by the biofilter, andby sulfuric acid generated by decomposition of hydrogen sulfide by thehydrogen sulfide oxidizing bacteria. The media desirably exhibits highretention of water, providing conditions that facilitate growth ofmicroorganisms. The media desirably exhibits high crushing force,allowing for it to be stacked in beds several feet thick without beingcompromised and broken. The media desirably exhibits a low resistance toairflow such that very little drop in pressure occurs through the bedvolume.

It has been discovered that sintered glass (SiO₂) media may be utilizedin place of traditional media materials in biofilters for the removal ofodorous compounds, for example, hydrogen sulfide, from contaminated air.The sintered glass media is formed from small glass beads, which in someembodiments have diameters similar to that of fine sand, for example, ina range of from about 8 μm to about 2,500 μm, in other embodiments, fromabout 25 μm to about 1,000 μm, and in other embodiments, diameters in arange of from about 50 μm to about 250 μm. The glass beads are packedinto a mold and heated to the point at which portions of the surfaces ofthe individual glass beads partially melt and become adhered to oneanother. The resulting sintered glass media includes a large number ofvoids and a low packing factor (the fraction of the volume of glasscompared to the volume of the sintered glass (glass plus void space inthe piece of media material)), for example, in some embodiments, apacking factor of between about 0.25 and about 0.9 and in otherembodiments a packing factor of between about 0.5 and about 0.8. In someembodiments, the resulting sintered glass media includes pores withcharacteristic dimensions (for example, diameters) of between about 1 μmand about 250 μm, and in other embodiments, between about 10 μm andabout 100 μm.

The large number of voids, pores, and low packing density of thesintered glass media provides the media with a large surface area onwhich bacteria may grow. The large surface area of the sintered glassmedia as compared to traditional media materials provides for thesintered glass media to operate with greater odor removal efficiency ina biofilter than media formed of traditional media materials. Theincreased odor removal efficiency of the sintered glass media may allowfor a biofilter utilizing sintered glass media to be sized smaller thana biofilter utilizing traditional media materials while achievingequivalent odor removal performance, or alternatively, to achievegreater odor removal performance than an equivalently sized biofilterutilizing traditional media material.

In some embodiments, a biofilter utilizing sintered glass media for thegas phase removal of hydrogen sulfide from contaminated air is operableto remove greater than about 95%, and in some instances greater thanabout 98% or greater than about 99%, of hydrogen sulfide fromcontaminated air including greater than about 50 ppm, and in someinstances greater than about 100 ppm, of hydrogen sulfide from thecontaminated air when passed through a media bed having a volume ofabout one cubic meter at a rate of greater than about 250 cubic metersper hour, and in some instances at a rate of greater than about 500cubic meters per hour. A biofilter utilizing sintered glass media forthe gas phase removal of hydrogen sulfide from contaminated air may alsobe operable to remove hydrogen sulfide from contaminated air atsubstantially the same efficiencies when the contaminated air includesconcentrations of hydrogen sulfide less than 50 ppm, for example,between about 0 ppm and about 50 ppm or between about 10 ppm and about40 ppm.

Sintered glass media has a low bulk density, for example, between about300 g/L and about 1,000 g/L in some embodiments and between about 500g/L and about 800 g/L in other embodiments. The low density of thesintered glass media makes handling of the sintered glass media lessdifficult than the handling of some traditional media materials.Further, the sintered glass media is non-reactive with and not attackedby sulfuric acid, and thus may exhibit a greater lifetime thantraditional media materials. Theoretically, sintered glass media mayhave an indefinite lifetime in a biofilter and may not need to beperiodically replaced due to breakdown caused by contact with sulfuricacid in the biofilter.

Sintered glass media for use in a biofilter may be formed in numerousshapes. In one embodiment, as illustrated in FIG. 4A, the sintered glassmedia is formed into hollow cylinders. In one exemplary embodiment, thesintered glass cylinders have an outside diameter of approximately 15mm, an inside diameter of approximately 10 mm, and a length ofapproximately 15 mm. In another exemplary embodiment, illustrated inFIG. 4B, the sintered glass media is formed into “gears” or a“gear-like” shape including a hollow and roughly cylindrical bodyapproximately 20 mm long with an outside diameter of approximately 26 mmand inside diameter of approximately 10 mm with cogs along both innerand outer walls. The outer cogs are about 5 mm by 5 mm placed about 2 mmapart for a total of 12 outer cogs. The inner cogs are about 1 mm by 1mm, spaced about 1 mm apart, for a total of 12 inner cogs. The sinteredglass media may also be formed into other shapes including, for example,rods, spheres, or any other regularly or irregularly shapedthree-dimensional structure. The dimensions above are representative ofparticular non-limiting embodiments. The sintered glass media may beformed into individual pieces having any dimensions desired.

It has also been discovered that silicon dioxide (SiO₂) based media maybe utilized in addition to or as an alternative to sintered glass mediain place of traditional media materials in biofilters for the removal ofodorous compounds, for example, hydrogen sulfide, from contaminated air.In some embodiments, foamed glass media is made in molds that are packedwith crushed or granulated glass mixed with a chemical agent, forexample, calcium carbonate or limestone. At the temperature at which theglass grains become soft enough to cohere, the agent gives off a gasthat is entrapped in the glass and forms a porous structure that remainsafter cooling. In some embodiments, the foamed glass media includessurface pores, and, in some embodiments, the foamed glass media includesvoids within the structure.

In some embodiments, the foamed glass media is formed by using re-cycledglass material which makes the foamed glass media more economical.Individual pieces of the foamed glass media may include one or morepassageways or channels extending from first surfaces of the individualpieces of the foamed glass media to second surfaces of individual piecesof the foamed glass media. The passageways or channels may be branchedor forked, may follow a tortuous path through the media, and may vary inwidth along their lengths and/or include other inhomogeneities. Anexample of a commercially available foamed glass media is Growstone®recycled foamed glass media, available from Growstone, Inc.

Further, although described above as being formed from SiO₂, sinteredmedia or foamed media in accordance with the present disclosure mayinclude various impurities or additives or may be formed from alternatematerials. For example, in some embodiments, the sintered or foamedglass media is formed from soda-lime glass which includes about 75%silicon dioxide (silica, SiO₂), sodium oxide (Na₂O), lime (CaO), andseveral minor additives, for example, magnesium oxide (magnesia, MgO)and aluminium oxide (alumina, Al₂O₃), from sodium borosilicate glass,which includes about 81% silica, about 12% boric oxide (B₂O₃), about4.5% sodium oxide (Na₂O), and about 2% alumina, or from aluminosilicateglass which includes about 57% silica, about 16% alumina, about 4% boricoxide, about 6% barium oxide (BaO), about 7% magnesia, and about 10%lime. In other embodiments other ceramics, for example, alumina orsilicon nitride (Si₃N₄), or elemental silicon may be formed into smallparticles or beads and sintered to form sintered media or processed toform foamed media for use in biofilters for the removal of H₂S or otherodorous or undesirable compounds from contaminated air.

FIG. 5 is an image of a sample of foamed glass media. As shown in FIG.5, the foamed glass media may be irregularly shaped with acharacteristic dimension of between about 0.5 inches (1.27 cm) and aboutone inch (2.54 cm). It should be appreciated, however, that foamed glassmedia particles having alternate dimensions and/or shapes from what isillustrated in FIG. 5 may be utilized. FIGS. 6A-6F are scanning electronmicroscope micrographs of the surface of examples of foamed glass media.As illustrated in FIGS. 6A-6F, the surface of the foamed glass media ishighly porous, with pores of various random sizes and shapes and havingcharacteristic dimensions of between about 25 μm and about 700 μm. Itshould be appreciated that foamed glass media with a different degree ofporosity and/or having pores of different characteristic dimensions mayalternatively or additionally be utilized in embodiments disclosedherein.

The large number of voids, pores, and low packing density of the foamedglass media provides the media with a large surface area on whichbacteria may grow. In some embodiments, the foamed glass media mayinclude up to about 80% or about 90% empty space. This high degree ofporosity both provides a large amount of surface area on which hydrogensulfide oxidizing bacteria may grow, and also provides the foamed glassmedia with a low density, for example, about 0.2 grams per cm³, whichmakes the media more lightweight than traditional biofilter media andthus easier to handle and transport. The large surface area of thefoamed glass media as compared to traditional media materials providesfor the foamed glass media to operate with greater odor removalefficiency in a biofilter than media formed of traditional mediamaterials. The increased odor removal efficiency of the foamed glassmedia may allow for a biofilter utilizing foamed glass media to be sizedsmaller than a biofilter utilizing traditional media materials whileachieving equivalent odor removal performance, or alternatively, toachieve greater odor removal performance than an equivalently sizedbiofilter utilizing traditional media material.

In some embodiments, a biofilter utilizing foamed glass media for thegas phase removal of hydrogen sulfide from contaminated air is operableto remove greater than about 95%, and in some instances greater thanabout 98% or greater than about 99%, of hydrogen sulfide fromcontaminated air including greater than about 50 ppm, and in someinstances greater than about 100 ppm, of hydrogen sulfide from thecontaminated air when passed through a media bed having a volume ofabout one cubic meter at a rate of greater than about 250 cubic metersper hour, and in some instances at a rate of greater than about 500cubic meters per hour. A biofilter utilizing foamed glass media for thegas phase removal of hydrogen sulfide from contaminated air may also beoperable to remove hydrogen sulfide from contaminated air atsubstantially the same efficiencies when the contaminated air includesconcentrations of hydrogen sulfide less than 50 ppm, for example,between about 0 ppm and about 50 ppm or between about 10 ppm and about40 ppm.

FIG. 7 is a flowchart that depicts a method 400 of operation of abiofilter according to one or more illustrative embodiments of theinvention. Although the operation of the biofilter is describedprimarily with respect to a routine that may be executed by a controller(e.g., controller 175 of FIG. 1), it should be appreciated that theinvention is not so limited, and many of the acts described below may beimplemented manually or batch-wise, for example, by a person, ratherthan by a controller, as discussed in more detail further below.

At act 410, a user may fill a media bed compartment of a biofiltervessel with media, for example, sintered glass media. In someembodiments, the sintered glass media is in the form of cylinder shapedmedia, and in other embodiments, gear shaped media and/or media of anyother desired shape may be utilized. In other embodiments, the media bedcompartment of the biofilter vessel is filled with foamed glass media asdisclosed herein in addition to or as an alternative to the sinteredglass media.

At act 420, an initial flow rate and or frequency of addition of waterand/or nutrients to the biofilter is set. These parameters may be setthrough a user interface, for example, input device 208 of a controllerfor the biofilter and may be stored in a memory of the controller. Theinitial parameters may be determined from historical data from othersimilar biofilters.

In act 430, the media is allowed to acclimate. Acclimation of the mediamay include flowing moist, bacteria laden contaminated air from a sewagesystem or other location where the biofilter is installed through thebiofilter vessel. Nutrients and water may be periodically added to thebiofilter vessel to provide an environment conducive for growth of adesirable bacterial population. Bacteria will adhere to the media in themedia bed and multiply by consuming the provided nutrients and hydrogensulfide from the contaminated air flowed through the biofilter.Additionally or alternatively, a desirable species of bacteria may beadded directly to the media bed by an operator.

At act 440, it is determined whether the media has completedacclimation. Completion of acclimation may be determined by comparing aconcentration of hydrogen sulfide exiting the biofilter to aconcentration of hydrogen sulfide in contaminated air entering thebiofilter. A reduction in hydrogen sulfide concentration of about 95% ormore may be indicative of the media being acclimated. Additionally oralternatively, production of sulfuric acid by the bacteria may providean indication of completion of acclimation of the media. The pH of fluidwithin the biofilter and/or waste fluid exiting a fluid outlet of thebiofilter may be monitored. When the fluid reaches a pH below athreshold value, for example, below about 4, below about 2.2 or betweenabout 1.8 and about 2.2, this may be indicative of the media beingacclimated.

Upon completion of acclimation of the media, the biofilter may beginnormal operation for removing H₂S and/or other undesirable compoundsfrom air passed through the biofilter (act 450). During operation,various parameters of fluid within the biofilter and/or exiting thebiofilter from the drain 170 of the biofilter vessel may be measured byvarious sensors and information regarding the measurements provided to acontroller of the biofilter to determine if adjustment of any operatingparameters is warranted, and if so, to adjust the relevant operatingparameters. For example, the concentration of nutrients or a componentof nutrients in fluid within the biofilter and/or exiting the biofilterfrom the drain of the biofilter vessel may be measured by a nutrientconcentration monitor and compared to a desired range of concentrationvalues by the controller (act 460). If the nutrient concentration of thefluid within the biofilter and/or exiting the biofilter from the drainof the biofilter vessel is outside the desired range, the controller mayadjust the flow rate and/or frequency of addition of nutrients to thebiofilter vessel (act 465). For example, if the nutrient concentrationof the fluid within the biofilter and/or exiting the biofilter from thedrain of the biofilter vessel is above an upper threshold, this may beindicative of an excessive amount of nutrients being provided to thebiofilter vessel. If the nutrient concentration is above this upperthreshold, the flow rate and/or frequency of addition of nutrients tothe biofilter vessel may be decreased. If the nutrient concentration ofthe fluid within the biofilter and/or exiting the biofilter from thedrain of the biofilter vessel is below a lower threshold, this may beindicative of an insufficient amount of nutrients being provided to thebiofilter vessel. If the nutrient concentration is below this lowerthreshold, the flow rate and/or frequency of addition of nutrients tothe biofilter vessel may be increased. The flow rate and/or frequency ofaddition of nutrient to the biofilter vessel may be adjusted until thenutrient concentration of the fluid within the biofilter and/or exitingthe biofilter from the drain of the biofilter vessel is in a rangebetween the upper and lower threshold values.

Although several of the acts described herein have been described inrelation to being implemented on a computer system or stored on acomputer-readable medium, it should be appreciated that the invention isnot so limited. Indeed, any one or more of the acts may be implementedby, for example, an operator, without use of an automated system orcomputer. For example, the measuring of the parameters of the fluidwithin and/or exiting the biofilter from the drain of the biofiltervessel may be performed by a human operator, and based upon thoseparameters, that operator, or another operator may manually adjustamounts or frequency of addition of the water and/or nutrients to thebiofilter vessel. Moreover, the determinations made at acts 440, 460,470, and/or 480 may be performed by a person, perhaps with the aid of asimple flow chart. Accordingly, although the method 400 was describedprimarily with respect to being implemented on a computer, it should beappreciated that the invention is not so limited.

It should be appreciated that numerous alterations, modifications, andimprovements may be made to the illustrated method. For example, any ofthe acts of the method 400 may be performed in alternate orders thanillustrated. Any one or more of the acts illustrated may be omitted fromembodiments of the method 400 and in some embodiments, additional actsmay be performed.

Example 1A Testing of Cylindrical Sintered Glass Media

Testing was performed to evaluate the performance of sintered glassmedia for the removal of hydrogen sulfide from contaminated air in abiofilter as described herein. The media was formed as cylinders havingan outside diameter of approximately 15 mm, an inside diameter ofapproximately 10 mm, and a length of approximately 15 mm. The media weretrialed in a stock Zabocs® ZB30 vessel using a side stream of foul airwithdrawn from the wet well at a lift station in southwest Florida. TheZabocs® ZB30 vessel had a cross sectional area of 4.9 ft² (0.455 m²) andincluded a single media bed with a height of 31.5 inches (0.8 m) and atotal volume of 12.9 ft³ (0.365 m³). Airflow through the vessel wasapproximately 100 cfm (cubic feet per minute, 170 m³/h).

The site was visited on a regular twice weekly schedule at which timeoperation parameters were observed and adjustments were made to optimizethe system. These parameters included inlet and outlet concentrations ofhydrogen sulfide, water, and nutrient spray schedule and flow rate, pH,temperature, and nutrient concentration of the water in the vessel, rateof air flow through the vessel, and pressure drop across the vessel. Fanspeed was adjusted to maintain the vessel at design hydraulic capacityper Pitot tube pressure differential measurements.

Recording hydrogen sulfide monitors (OdaLog® portable gas detectors fromApp-Tek International) were deployed to record the hydrogen sulfideconcentration in air introduced into the vessel and output from thevessel every five minutes, so that average and maximum hydrogen sulfideconcentrations could be observed on a daily basis.

The Zabocs® ZB30 vessel was filled with cylindrical sintered glassmedia. The evaluation of the performance of the biofilter including thecylindrical sintered glass media was performed over a seven monthperiod.

The cylinders required very little acclimation time. On startup thehydrogen sulfide removal rate was over 95% in the first 24 hours andimproved to 99% within four days.

Spikes in the influent hydrogen sulfide concentration causedbreakthrough to the exhaust of unacceptable hydrogen sulfideconcentrations and percent removal decreased.

During winter months in the middle of the testing period the efficiencyof hydrogen sulfide removal was significantly less than the 99% removalrate target. It is assumed that this was due to the effect of lowertemperatures on the metabolism of the bacteria in the biofilter.

At several points during the testing, the hydrogen sulfide removal ratedropped below 90%. These drops in hydrogen sulfide removal rate were dueto operation failures, including two incidents of increase in influenthydrogen sulfide concentration requiring re-acclimation of thebiofilter, and a few instances of the nutrient supply failing. All dateswhen removal fell to less than 90% were accompanied by operatingproblems and errors.

The results of the testing of the cylindrical sintered glass media aresummarized in Table 1 below and in the chart in FIG. 6.

TABLE 1 Average Average Average Daily Daily Daily Daily Daily Daily %Average Average Average Maximum Maximum Removal at H₂S In H₂S Out % H₂SIn H₂S Out Maximum Media (ppm) (ppm) Removal (ppm) (ppm) H₂S InCylindrical 91 2.25 97.5 168 14.5 91.4 Sintered Glass

Example 1B Testing of Gear-Shaped Sintered Glass Media

After testing of the cylinder media was completed, the cylinder mediawas removed from the Zabocs® ZB30 vessel which was then filled with 80centimeters (31.5 inches) of gear shaped sintered glass media asillustrated in FIG. 4B. The gear shaped sintered glass media included aroughly cylindrical body approximately 20 mm long with an outsidediameter of approximately 26 mm and inside diameter of approximately 10mm with cogs along both inner and outer walls. The outer cogs are about5 mm by 5 mm placed about 2 mm apart for a total of 12 outer cogs. Theinner cogs are about 1 mm by 1 mm, spaced about 1 mm apart, for a totalof 12 inner cogs. The average daily hydrogen sulfide removal rate was17% when the vessel was put into operation and improved each day untilreaching 100% after 11 days of operation. The vessel then maintained anaverage daily removal rate of 98.8%, and no days with less than 97.5%.The average influent hydrogen sulfide concentration was 55.8 ppmv (partsper million by volume) and the average exhaust hydrogen sulfideconcentration was 0.7 ppmv. During that same period the average dailypeak influent hydrogen sulfide concentration was 118 ppmv and theaverage daily peak exhaust hydrogen sulfide concentration was 2.5 ppmvgiving an average of 98.0% removal at peak loading.

The results of the testing of the gear shaped sintered glass media aresummarized in Table 2 below and in the charts in FIGS. 7-10.

TABLE 2 Average Average Average Daily Daily Daily Daily Daily Daily %Average Average Average Maximum Maximum Removal at H₂S In H₂S Out % H₂SIn H₂S Out Maximum Media (ppm) (ppm) Removal (ppm) (ppm) H₂S In GearShaped 55.8 0.8 98.8 118 2.5 98.0 Sintered Glass

Discussion Pressure Drop

The pressure drop across the media bed remained low at under 0.5 incheswater column (iwc) for the cylinder shaped media and under 0.1 iwc forthe gear shaped media. This indicates little, if any, media breakdown,and open free flow through the media.

Low Hydrogen Sulfide Removal Rate

The data collected shows a decrease in hydrogen sulfide removal rateduring cold months for the cylinder shaped media. The rate slowlydecreased to 90% and below, and then increased as spring arrived. Uponreview of all data collected over the course of the testing of thecylinder shaped media, the media failed to meet 99% hydrogen sulfideremoval during cold weather even though all key performance indicatorswere within the optimal values used for other media. This was not thecase when using the gear shaped media as it was only tested duringrelatively cold weather of February and March. Without being bound to aparticular theory, it is surmised that the gear shaped media exposesmore surface area, allowing exposure of more bacteria to air flowedthrough the media bed.

The watering system was the adjusted to run at a frequency to keep themedia moist and for a period to maintain drain pH in the range from 1.8to 2.2 and drain NO₃—N concentrations between 2 ppm and 10 ppm. Wheneverthe pH varied outside this range, removal was hampered. Likewise, ifinsufficient nutrient was supplied and nitrate was not found in thedrain water, hydrogen sulfide removal was negatively affected.

Insufficient bulk density (too much open space in the media) may alsohave been the cause of lower removal rates for the cylinder shapedmedia. Since the media has a great amount of open space, contaminatedair may have been more likely to pass through the bed untreated thanwhen utilizing media having a less open structure.

Acclimation

The fast acclimation of the cylinder shaped material and high hydrogensulfide removal early in testing was extremely promising. The surface ofthe media did not have a visible biological film, so without being boundto a particular theory, it is surmised that the acclimation of the mediamay have been caused by a process other than bacteria oxidizing hydrogensulfide to form sulfuric acid.

The fast acclimation may have been due in part to adsorption. The smallpores in the surface of the sintered glass would cause capillary actionto naturally occur. Once the water in the pores was saturated in H₂S,the hydrogen sulfide removal would have dropped.

Whatever the initial H₂S removal mechanism may have been, the highinitial media performance dropped off and then slowly increased to anacceptable level. Adjustments continued to attain optimum operatingconditions.

The gear shaped media did not exhibit the same immediate high hydrogensulfide removal rate as the cylinder shaped media, but rather exhibitedan acclimation period over a similar period of time as other mediacommonly used in biofilters.

Example 1A, 1B Conclusions

The cylinder shaped sintered glass media does not show signs ofbreakdown after operation of over six months. Likewise the gear shapedmedia, though tested for a shorter period of time, has shown no signs ofbreakdown.

Sintered glass media exhibits high rates of H₂S removal fromcontaminated air, and thus has potential for use as a biofilter mediahaving superior properties, for example, lower density, longer servicelife, and higher H₂S removal efficiency than traditional filter media.

The cylinder shaped media configuration may contain too much open spacethrough which foul air can channel without treatment. The gear shapedmedia exhibited better H₂S removal efficiency than the cylinder shapedmedia.

Example 2A Testing of Foamed Glass Media at Site 1

Testing was performed to evaluate the performance of foamed glass mediafor the removal of hydrogen sulfide from contaminated air in a biofilteras described herein. The media used was Growstone® foamed glass media.The media were trialed in a stock Zabocs® 4000 biofilter, available fromEvoqua Water Technologies LLC, using a side stream of foul air withdrawnfrom the wet well at a lift station in southwest Florida. The Zabocs®4000 biofilter vessel had a cross sectional area of 16 ft² (1.49 m²) andincluded upper and lower media beds with a heights of 48 inches (1.21 m)and a total volume of 64 ft³ (1.81 m³).

Monitoring of the performance of the Zabocs® biofilter was performedfrom July 2014 through April 2015. The site was surveyed weekly andhydrogen sulfide data loggers (OdaLog® portable gas detectors) weredeployed to determine biofilter performance.

Hydrogen sulfide concentrations from the influent, from the spacebetween media beds, and from the exhaust was measured continually andrecorded every five minutes. The data from the OdaLog® portable gasdetectors was collected, processed, saved, and recorded along with allother data collected.

The foamed glass media was installed during a media exchange on Jul. 18,2014 by removing the spent media from the biofilter and replacing itwith 64 ft³ (1.8 m³) of the foamed glass media. The biofilter wasstarted at 50% of design air flow, operating at approximately 175 cfm(297 m³/h). On July 22 the hydrogen sulfide removal rate was 91%. OnJuly 26 the hydrogen sulfide removal rate was 96%, on July 27 and 28 thehydrogen sulfide removal rate was 98%, and on July 29 the target of 99%hydrogen sulfide removal was attained with 98 ppmv hydrogen sulfide inthe influent stream and 1.2 ppm in the effluent stream. On July 29 thepeak hydrogen sulfide in the influent stream was 204 ppmv with a peakexhaust hydrogen sulfide of 8.4 ppmv for 96% removal at peak. Duringthis eleven day period adjustments and corrections were performed sothat the system reached full acclimation three days after finaladjustment.

Over the next seven months the system operated at the targeted hydrogensulfide removal rate with several exceptions. In each of these instanceseither some operating parameter was out of adjustment or theconcentration of influent hydrogen sulfide drastically increased ordecreased over a short period of time. Once corrected, the biofilterreturned to achieving a 99% hydrogen sulfide removal rate.

On March 15 the top access port on the vessel blew out relieving backpressure from the carbon drums and the system operated for five days at499 cfm (848 m³/h), 150 cfm greater than design. The hydrogen sulfideremoval rate dropped to between 95% and 97%. Following replacement ofthe access port and reacclimation, removal of hydrogen sulfide met the99% removal rate specification until monitoring halted on April 15.

Data illustrating hydrogen sulfide removal with the biofilter utilizingthe foamed glass media for an exemplary one week period is shown in thegraph of FIG. 13.

Discussion Nutrient

During this trial, on two occasions there was no nitrate residual in thedrain water, once due to a nutrient pump failure, and once due to aplugged eductor. In both cases, in the absence of nutrient, the hydrogensulfide removal rate of the biofilter decreased.

Drain pH

The drain pH of the biofilter correlated with both the influent hydrogensulfide concentration and the amount of water contacting the media. If ahigh influent of hydrogen sulfide was observed, generally an average ofover 100 ppmv, drain water pH tended to be low. Instances where drain pHwas above 2.2 were far more common due to hydrogen sulfide concentrationbelow the expected 100 ppmv.

It is important to note that the pH will naturally fluctuate based onthe incoming hydrogen sulfide concentration. Therefore, depending on thetime of day and any other factors that affect wet-well hydrogen sulfideconcentrations, a surveyor may get varied results from visit to visit,even when no operating parameters have changed.

Pressure Drop

After 9 months of operation, the pressure drop across the vessel was 0.4iwc, the same as it was two weeks after start-up. That, along withfailure to observe changes in the media or bed height, indicates thatthe foamed glass media does not readily decompose.

Hydrogen Sulfide Removal Rate

As previously stated, low hydrogen sulfide removal rates correlateddirectly to low nutrient levels in the drain, out of range drain waterpH, low influent hydrogen sulfide concentrations, and air flow greaterthan design.

Additionally, hydrogen sulfide removal rate may be low when influenthydrogen sulfide concentration is very high or has very high peak(maximum) concentrations. The bacteria in the biofilter are limited asto the quantity of hydrogen sulfide they can consume. The population ofthe culture is limited by the amount of hydrogen sulfide available, andthe ability of the culture to remove hydrogen sulfide depends on itspopulation. The culture population will adjust to the amount of hydrogensulfide, but the adjustment time is generally measured in hours,sometimes days. The biofilter utilized in this testing was designed foroperation with an influent of 100 ppmv H₂S at 350 cfm. If there areextremely high peaks, the bacteria cannot perform to the requiredcapacity. Lower concentrations are more difficult to achieve 99% removalsince the effluent concentrations required are so low.

Example 2B Testing of Foamed Glass Media at Site 2

Testing was performed to evaluate the performance of foamed glass mediafor the removal of hydrogen sulfide from contaminated air in a biofilteras described herein. The media used was Growstone® foamed glass media.The media were trialed in a stock Whisper® 72 biofilter, available fromEvoqua Water Technologies LLC, using a side stream of foul air withdrawnfrom the wet well at a lift station in southwest Florida. The Whisper®72 biofilter vessel had a cross sectional area of 28.3 ft² (2.63 m²) andincluded upper and lower media beds with a total height of 57 inches(1.45 m) and a total volume of 134 ft³ (3.8 m³).

On Aug. 14, 2014, a Whisper® 72 biofilter was installed at a liftstation in southwest Florida. It was filled with 134 ft³ (3.8 m³) ofGrowstone® foamed glass media distributed in two beds. Over the nextnine months performance was continually monitored by OdaLog® portablegas detectors deployed on-site and weekly visits surveyed the operatingparameters of the system.

The Whisper® 72 biofilter with foamed glass media was installed on Aug.14, 2014. The biofilter was started at approximately one-third of designair flow, operating at approximately 200 cfm (340 m³/h) of a design airflow of 600 cfm (1,019 m³/h). At two weeks the flow was increased totwo-thirds of design, 400 cfm (680 m³/h). Data for the first month ofoperation indicated poor hydrogen sulfide removal, ranging from 70% to95% removal. A design flaw was noted that the single pigtail nozzle forthe bottom bed gave a pattern such that an estimated 80% of the watersprayed the inner one-half diameter of the vessel and even in circlesconcentric from the nozzle, the water spray was uneven and thatchanneling was occurring. On Mar. 23, 2015, the single pigtail spraynozzle on the bottom bed was replaced with an improved design sprayapparatus such that the bed surface received approximately the sameamount of water and nutrient per unit surface area of the media. The topnozzle was timed to operate less than one percent of the time that thebottom water was on. Within three days the bed had acclimated so that onMarch 28 the average daily hydrogen sulfide removal rate was 99.7%. Inthe sixty days after that, the hydrogen sulfide removal rate was equalto or greater than 99% for fifty-eight of the sixty days. Both days thatthe goal was missed there were sudden increases in the load on thesystem. The first day that the goal was missed was May 18, the day whenthe air flow was increased from 438 cfm (744 m³/h) to 625 cfm (1,062m³/h), yet the hydrogen sulfide removal rate was 97%. Within twenty-fourhours the media had acclimated to the increased flow. Then, on May 23the concentration of hydrogen sulfide in the air stream jumped from amorning average of 37 ppmv before 10:00 AM to 199 ppmv average for therest of the day. On that day the hydrogen sulfide removal rate was 95%.The unusually high concentration of hydrogen sulfide from the wet wellcontinued for two more days, yet the biofilter acclimated and returnedto achieving a 99% hydrogen sulfide removal rate by the following day.

Data illustrating hydrogen sulfide removal with the biofilter utilizingthe foamed glass media for a one week period including the May 18 andMay 23 excursions is shown in the graph of FIG. 14.

Discussion Nutrient

During this trial there it was observed that maintaining nutrientconcentrations such that nitrate nitrogen was at least 5 ppm allowed thebiofilter unit to operate efficiently.

Drain pH

The drain pH of the biofilter unit correlated with both the influenthydrogen sulfide concentration and the amount of water contacting themedia. If an increase in the influent concentration of hydrogen sulfidewas observed, drain pH tended to drop. If a decrease in hydrogen sulfideconcentration was observed, the pH would rise.

It is important to note that the pH will naturally fluctuate based onthe incoming hydrogen sulfide. Therefore, depending on the time of dayand any other factors that affect wet-well hydrogen sulfideconcentrations, a surveyor may get results varied by 0.1 or even 0.2from visit to visit, even when no operating parameters have changed.

Pressure Drop

After 9 months of operation, the pressure drop across the vesseloperating at design air flow of 600 cfm (1,019 m³/h) is 2.3 iwc. That,along with failure to observe changes in the media or bed height,indicates that the foamed glass media has been stable for nine monthsand does not readily decompose in the conditions within the operatingbiofilter.

Hydrogen Sulfide Removal Rate

Low hydrogen sulfide removal rates correlated directly to unevendistribution of water and nutrient across the media bed, low nutrientlevels in the drain, out of range drain water pH, and low influenthydrogen sulfide concentrations.

Additionally, hydrogen sulfide removal rate may be low when influenthydrogen sulfide concentration is very high above design or has veryhigh peak (maximum) concentrations. The bacteria in these units arelimited as to the quantity of hydrogen sulfide they can consume. For theWhisper® 72 biofilter utilized in this test, was designed for operationwith 100 ppmv H₂S at 600 cfm. If there are extremely high peaks inhydrogen sulfide concentration, the bacteria cannot perform to therequired capacity. Increases in concentration of hydrogen sulfide over ashort period of time will result in lowered efficiency of the biofilter,but the biology can acclimate and achieve 99% removal within 24 hoursfrom an immediate jump in concentration to 200 ppmv, twice the designconcentration. Lower concentrations are more difficult to achieve 99%removal since the effluent concentrations required are so low.

Example 2A, 2B Conclusions

Foamed glass media exhibits high rates of H₂S removal from contaminatedair, and thus has potential for use as a biofilter media having superiorproperties, for example, lower density, longer service life, and higherH₂S removal efficiency than traditional filter media.

Foamed glass media is stable and does not readily break down in abiofilter. Extrapolating from nine months data, media change-out shouldnot be required for at least five years.

Example 3 Biofilter Acclimation Study

Testing was performed to evaluate removal of hydrogen sulfide fromgaseous effluent from a lift station wet-well located in southwestFlorida using a Whisper® 96 biofilter with recycled foamed glass media.The Whisper® 96 biofilter has a diameter: 96 inches (2.44 m), a totalbed depth of 57 inches (1.45 m), a cross-sectional area of 50.3 ft²(4.67 m²), and a total bed volume of 239 ft³ (6.77 m³). Parameters ofthe wet well were as indicated in Table 3 below:

TABLE 3 Well Diameter Well Depth Well Volume Avg. Sulfides in Air (ft)(ft) (ft³) (ppm) 12 20 2262 338

The Whisper® 96 biofilter system was designed to operate at an air flowfrom 0 to 280 cfm (0 to 476 m³/h), and under average H₂S loadings of300-500 ppm. Foamed glass media made from recycled glass was implementedin both the upper and lower beds of the biofilter to serve as growthsites for the sulfide oxidizing bacteria.

The biofilter system was sized to exchange air in the wet well six timesper hour. It was predicted that the highly porous recycled foamed glassmedia would provide adequate bacterial growth to reduce sulfidesdischarged in air to <1 ppm, or achieve a 99% percent sulfide removal(whichever discharge value was greater).

The Biofilter was installed on May 31st and started-up Apr. 1, 2015.Surveys of the system were performed over several weeks following thestart-up of the Whisper® 96 biofilter unit. Data from these surveys areprovided below in Table 4 below:

TABLE 4 Inlet H₂S Outlet H₂S Percent Days after ConcentrationConcentration Sulfide Date Start-up (ppm) (ppm) Removal Apr. 3, 2015 270 60 14.3% Apr. 15, 2015 14 90 30 66.7% Apr. 24, 2015 23 90 0.7 99.2%Apr. 29, 2015 28 40 0.2 99.5%

Discussion Acclimation

It can be seen that following a few days of start-up, the system quicklyresponded to sulfide in air pulled from the wet-well, and began toremove H₂S. By the end of the third week, the target goal of 99% removalwas achieved and the system was fully acclimated. FIG. 15 shows theacclimation response of the system using the data recorded above.

Sulfide Removal

With the system optimized, hydrogen sulfide concentrations from the liftstation wet well and in the biofilter were as indicated in Table 5below. It should be noted that the majority of the sulfide is removed bythe first bed. This indicates high levels of bacterial activity in thelower portion of the unit.

TABLE 5 Gastec Sulfide Measurements From Well Inlet Middle Outlet H₂S120 ppm 41 ppm 7 ppm 0.2 ppm Concentration (ppm) Percent 0% 0% 82.9%99.5% Removal (%)

Nutrient

Residual nitrate in the drain water from the biofilter was observed tobe approximately 0 ppm. This nitrate residual is low, and nutrient feedshould be adjusted to have a residual of −5 ppm.

Drain pH

The pH of the drain water was 2.17 (optimum range 1.8-2.2), with atemperature of 25.9° C.

Pressure Drop

Pressure drop of 1.20 iwc across the blower was measured using an Extechdigital manometer, which was well within an acceptable range.

Conclusions

The results of this study show that foamed glass media may beeffectively used in a biofilter to remove hydrogen sulfide fromcontaminated air. The bacterial population on the foamed glass mediaacclimates quickly, and upon acclimation is capable of removing morethan 99% of hydrogen sulfide from contaminated air passed through themedia.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Anyfeature described in any embodiment may be included in or substitutedfor any feature of any other embodiment. Such alterations,modifications, and improvements are intended to be part of thisdisclosure, and are intended to be within the scope of the invention.Accordingly, the foregoing description and drawings are by way ofexample only.

What is claimed is:
 1. A gas phase biofilter for the treatment ofcontaminated air, the biofilter comprising: a contaminated air inlet; atreated air outlet; and a media bed including foamed glass media influid communication between the contaminated air inlet and the treatedair outlet, the foamed glass media having a density of about 0.2grams/cm³.
 2. The biofilter of claim 1, wherein the foamed glass mediacomprises silicon dioxide.
 3. The biofilter of claim 2, wherein thefoamed glass media includes surface pores.
 4. The biofilter of claim 3,wherein the foamed glass media includes internal voids.
 5. The biofilterof claim 4, wherein individual pieces of the foamed glass media includepassageways extending from first surfaces of the individual pieces tosecond surfaces of the individual pieces.
 6. The biofilter of claim 1,wherein the foamed glass media comprises recycled glass.
 7. Thebiofilter of claim 1, further comprising a population of hydrogensulfide oxidizing bacteria disposed on the foamed glass media.
 8. Thebiofilter of claim 7, operable to reduce a concentration of hydrogensulfide in contaminated air including greater than 100 ppm hydrogensulfide by more than about 95% when the contaminated air is passedthrough the media bed of the biofilter at a flow rate of from zero to500 cubic meters per hour per cubic meter of media bed volume.
 9. Thebiofilter of claim 7, operable to reduce the concentration of hydrogensulfide in the contaminated air including greater than 100 ppm hydrogensulfide by more than about 95% when the contaminated air is passedthrough the media bed of the biofilter at a flow rate of greater thanabout 500 cubic meters per hour per cubic meter of media bed volume. 10.The biofilter of claim 8, operable to reduce the concentration ofhydrogen sulfide in the contaminated air by more than about 99% when thecontaminated air is passed through the media bed of the biofilter at aflow rate of from zero to 500 cubic meters per hour per cubic meter ofmedia bed volume.
 11. The biofilter of claim 9, operable to reduce theconcentration of hydrogen sulfide in the contaminated air by more thanabout 99% when the contaminated air is passed through the media bed ofthe biofilter at a flow rate of greater than about 500 cubic meters perhour per cubic meter of media bed volume.
 12. A method of removing anundesirable compound from contaminated air, the method comprisingflowing the contaminated air through a gas phase biofilter including afoamed glass media, the foamed glass media having a density of about 0.2grams/cm³.
 13. The method of claim 12, further comprising at leastpartially filling a media bed compartment of the biofilter with thefoamed glass media prior to flowing the contaminated air through thebiofilter.
 14. The method of claim 13, further comprising facilitatinggrowth of a population of hydrogen sulfide oxidizing bacteria on thefoamed glass media.
 15. The method of claim 14, further comprisingmaintaining the population of hydrogen sulfide oxidizing bacteria on thefoamed glass media.
 16. The method of claim 14, further comprising:measuring a concentration of nutrient in one of a fluid within andexiting the biofilter; and adjusting an amount of nutrient added to themedia bed compartment per unit of time responsive to the concentrationof the nutrient in the fluid being outside of a predetermined range. 17.The method of claim 12, wherein removing the undesirable compound fromthe contaminated air comprises removing hydrogen sulfide from thecontaminated air.
 18. The method of claim 17, wherein removing thehydrogen sulfide from the contaminated air comprises reducing aconcentration of hydrogen sulfide by passing the contaminated air at aflow rate of from about zero to about 250 cubic meters per hour percubic meter of a media bed of the biofilter including the foamed glassmedia through the media bed.
 19. The method of claim 18, whereinreducing the concentration of hydrogen sulfide in the contaminated aircomprises reducing the concentration of hydrogen sulfide in thecontaminated air by more than about 99%.
 20. The method of claim 17,wherein removing the hydrogen sulfide from the contaminated aircomprises reducing a concentration of hydrogen sulfide by passing thecontaminated air at a flow rate of greater than about 500 cubic metersper hour per cubic meter of the media bed through the media bed.